Ion exchange resins used in high pressure chromatography columns are desired that can withstand the relatively high pressures and/or high temperatures typically encountered. Higher pressures can often impart greater separation power. Such ion exchange resins are usually crosslinked to provide resilience to deformation or fracture under high pressure and/or high temperature conditions. For example, many commercially available ion exchange resins for high pressure separations are based on divinylbenzene crosslinked polystyrene that are functionalized to provide ionic groups.
For some applications, it is desirable that the ion exchange resins be porous. Porous materials with micropores (i.e., pores less than 2 nanometers) can be particularly useful for some separations. The micropores can lead to increased capacity, improved kinetics of interaction with charged materials and ions, or both. Porous ion exchange resins have been prepared by the addition of a sulfonic acid group to polymeric materials prepared from divinyl benzene. Such materials are described, for example, in Liu et al., Journal of Catalysis, 2010, 271, 52-58. While these materials can contain some micropores, the majority of the pores tend to be in the mesopore range (e.g., 2 to 50 nanometer pore diameter).
Polymeric materials that are porous have been prepared using spirobisindane-containing materials. For example, Reaction Scheme A shows the reaction of 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane with 2,3,5,6-tetrafluoroterephthalonitrile to form a polymeric material with fused dioxin rings as linking groups. These polymers and their synthesis methods are described more fully, for example, in Budd et al., Chem. Commun., 2004, 230 and in U.S. Pat. No. 7,690,514 (McKeown et al.).
These polymeric materials have a rigid backbone containing regular points of contortion. This characteristic of the backbone results in poor packing of the polymeric chains with each other. The interstitial space between the polymer chains tends to result in microporosity. These polymeric materials are not suitable, however, for applications that require large volumes of material. The polymerization times tend to be lengthy (e.g., several days) and the monomers used to form the polymers are often quite expensive.